buglist 7142 exp^log(x) Cannot take first of an empty list update

The error apparently comes from EXPR where the implementation is
  x**y == exp(y * log(x))

so exp^log(x) is computed as

  exp(log(x) * log(exp))

which should be ok, but then the system handles log exp and tries to simplify it
to the identity map, and not finding the argument.